In the prior art, use of a stylus-based roughness tester to determine the roughness of a surface is known.
However, this type of test takes a relatively long time to carry out, because the roughness must be measured, using a contact technique, segment by segment.
In addition, because of the size of styluses, it is not possible to detect defects of less than a certain size and the smaller the defects to be detected, the longer the measurements take.
It is also known to use other techniques such as electron, optical or near-field microscopy, and techniques based on the scatter of light in the far field.
These techniques allow a rapid inspection of surface finishes, which may be carried out in a short amount of time.
Among these techniques, those based on the scatter of light in the far field in particular seem to be advantageous, because they are nonintrusive and because they allow the consequences of scattering effects governed by the wave theory of light to be used to extract, almost instantaneously, derived properties of the surface of the examined part, allowing irregularities such as small scratches or local roughness that would be completely invisible to the naked eye to be detected.
To do this, the light that an object/sample to be observed scatters in every direction of space, in reflection or transmission, is first measured, for example using an integrating sphere to take a single measurement of the integrated total scattering in every direction of space.
However, such characterization proves to be unsatisfactory, in particular because it does not take into account the notion of passband or spatial resolution.
To overcome this difficulty, measuring techniques have been developed that measure the scattered light emitted by the sample in each direction of space. Angular resolved scattering (ARS) then being spoken of.
However, to obtain a precise result, a scan of scattering angle must be performed, this requiring a precise mechanical mechanism for moving the detector of scattered light; not only are such systems complex and expensive but also the process of analysis is once again quite slow.
Lastly, an integrating hemisphere equipped at its apex with a sensor for measuring scattered light and with several tens of light sources that are distributed over the hemisphere and that allow the object/sample to be analyzed to be illuminated from various angles is known.
In this case, each light source is turned on in turn and an image of the light scattered by each of the light sources is taken. Therefore, as many images of scattered light as there are light sources fastened to the hemisphere are obtained. Although this method is very precise, it requires a very large volume of data to be dealt with, this making it too slow for certain industrial processes.